The economic argument for adopting energy efficiency measures, often called the low-hanging fruit' in climate mitigation, has also been studied to be of big potential. The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) suggests global emissions could double or even triple by mid-century. Many governments, especially in countries with large emission footprints, are still lagging far behind in diffusing these technologies. Addressing the technical question is only one part of the equation; providing a sound economic basis for the transition is another essential aspect in making the most optimistic argument for rapid sustainable energy transition. The technology is also beyond commercial diffusion, a key criterion for the Rapid Mitigation Project. The technology could fall into the wrong hands. The threat of a nuclear war can only divide attention to rapid climate mitigation. At a time when rapid climate mitigation is required, options that present fewer risks to society should be given priority in decision-making.